Our hypothesis is that mechanical stress, accompanying the elevated intraocular pressure (IOP)-associated changes in outflow pathway tissue morphology, induces the release from outflow pathway cells of factors known to modulate vascular endothelial cell permeability, such as cytokines and reactive oxygen species; that these factors increase the permeability of the inner wall of Schlemm's canal (SC); and that the increase in pore density and/or average pore size associated with the enhanced permeability of the SC endothelium leads to a decrease in outflow resistance either directly, or from a reduction in the funneling effect (1) at the level of the juxtacanicular tissue (JCT). Our previous analysis of gene expression using single pass sequencing and gene arrays indicated that factors known to be induced by mechanical stress in a number systems, and which modulate permeability in the vascular system, kidney and intestine, are synthesized by the trabecular meshwork (HTM), (2,3). These studies also provided evidence that at least some of these factors can be induced after an increase in IOP (3). Given the "vascular" nature of SC (4-6), one of the possible effects of these factors in the outflow pathway would be to increase the permeability of the SC endothelium. Another important effect could be the remodeling of the extracellular matrix (ECM) in the JCT. However, changes in SC permeability are expected to occur faster than those involved in ECM remodeling, and may, therefore, constitute a primary effect. To test this hypothesis, we propose to: determine whether IL1beta, IL6, TGF-beta1, VEGF, SPARC and H2O2 are induced by increased pressure in the HTM of perfused human anterior segments (SA1: determine if these factors are capable of increasing the permeability of SC endothelium; (SA2); identify genes expressed in the SC cells that are not expressed in the SC cells that are not expressed in other cells of the outflow pathway (SA3); and use promoters from some of these genes to target the expression of constructs capable of mimicking the intracellular effects of the permeability factors in the SC cells in organ culture, and this way determine if changes in SC permeability correlates with effects on the facility of the outflow pathway in situ (SA4).